Electrically conducting polymers have been used in a variety of organic electronic devices, including in the development of electroluminescent (EL) devices for use in light emissive displays. With respect to EL devices, such as organic light emitting diodes (OLEDs) containing conducting polymers, such devices generally have the following configuration:                anode/buffer layer/EL polymer/cathodeThe anode is typically any material that has the ability to inject holes into the otherwise filled π-band of the semiconducting, EL polymer, such as, for example, indium/tin oxide (ITO). The anode is optionally supported on a glass or plastic substrate. The EL polymer is typically a conjugated semiconducting polymer such as poly(paraphenylenevinylene) or polyfluorene. The cathode is typically any material (such as, e.g., Ca or Ba) that has the ability to inject electrons into the otherwise empty π*-band of the semiconducting, EL polymer.        
The buffer layer is typically a conducting polymer and facilitates the injection of holes from the anode into the EL polymer layer. The buffer layer can also be called a hole-injection layer, a hole transport layer, or may be characterized as part of a bilayer anode. Typical conducting polymers employed as buffer layers include polyaniline (PANI) and polydioxythiophenes such as poly(3,4-ethylenedioxythiophene) (PEDT). These materials can be prepared by polymerizing the corresponding monomers in aqueous solution in the presence of a water soluble polymeric acid, such as poly(styrenesulfonic acid) (PSS).
The aqueous electrically conductive polymer dispersions synthesized with water soluble polymeric sulfonic acids have undesirable low pH levels. The low pH can contribute to decreased stress life of an EL device containing such a buffer layer, and contribute to corrosion within the device. Accordingly, there is a need for compositions and buffer layers prepared therefrom having improved properties.
Electrically conducting polyanilines are typically prepared by polymerizing aniline or substituted aniline monomers in aqueous solution by an oxidative polymerization using an oxidizing agent such as ammonium persulfate (APS), sodium persulfate or potassium persulfate. The aqueous solution contains a water soluble polymeric acid such as poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (“PAAMPSA”), PSS, and the like. In general, enough of the acid is present to form acid/base salts with emeraldine base of polyanilines, wherein formation of the acid/base salt renders the polyanilines electrically conductive. Thus, for example, emeraldine base of polyaniline (PANI) is typically formed with PAAMPSA to resulting in electrically conductive PANI/PAAMPSA.
Aqueous polyaniline dispersions are commercially available from Ormecon Chemie GmbH and Co. KG (Ammersbeck, Germany). It is known as D 1005 W LED. The polyaniline is made from aniline and water soluble poly(styrenesulfonic acid). The dried films obtained from D 1005 W LED re-disperse readily in water. The water becomes acidic with pH in the range of 1 at 2.5% (w/w). Films gain about 24.0% (w/w) moisture at ambient conditions.
Dried films from a lab batch aqueous dispersion of polyaniline/poly(2-acrylamido-2-methyl-1-propanesulfonic acid), are also readily re-dispersible in water. The polyaniline is made from aniline and a water soluble PAAMPSA.
Electrically conducting polymers also have utility as electrodes for electronic devices, such as thin film field effect transistors. In such transistors, an organic semiconducting film is present between source and drain electrodes. To be useful for the electrode application, the conducting polymers and the liquids for dispersing or dissolving the conducting polymers have to be compatible with the semiconducting polymers and the solvents for the semiconducting polymers to avoid re-dissolution of either conducting polymers or semiconducting polymers. The electrical conductivity of the electrodes fabricated from the conducting polymers should be greater than 10 S/cm (where S is a reciprocal ohm). However, the electrically conducting polyaniline made with a polymeric acid typically provide conductivity in the range of ˜10−3 S/cm or lower. In order to enhance conductivity, conductive additives may be added to the polymer. However, the presence of such additives can deleteriously affect the processability of the electrically conducting polyaniline. Accordingly, there is a need for improved conductive polyaniline with good processability and increased conductivity.